Apparatus for microlithographic projection exposure and apparatus for inspecting a surface of a substrate

ABSTRACT

An apparatus ( 10 ) for microlithographic projection exposure, which includes: an optical system ( 18 ) for imaging mask structures ( 16 ) onto a surface ( 21 ) of a substrate ( 20 ) by projecting the mask structures ( 16 ) with imaging radiation ( 13 ) onto an exposure area of the substrate surface, and various structure defining a measurement beam path ( 36 ) for guiding measurement radiation ( 34 ). The measurement beam path ( 36 ) extends within the optical system ( 18 ) such that the measurement radiation ( 34 ) impinges on a measurement area on the substrate surface that is offset from the exposure area.

This is a Continuation of U.S. application Ser. No. 12/895,747, whichwas filed on Sep. 30, 2010, which is a Continuation of InternationalApplication PCT/EP2009/002302, with an international filing date of Mar.30, 2009, which was published under PCT Article 21(2) in German. Thecomplete disclosures of both these applications are incorporated intothe present application by reference. The present application claims thepriority of German Patent Application 10 2008 017 645.1 and of U.S.Provisional Patent Application 61/072,980, both filed on Apr. 4, 2008,and the entire contents of which are also incorporated into the presentapplication by reference.

FIELD OF AND BACKGROUND OF THE INVENTION

The invention relates to an apparatus for microlithographic projectionexposure and to a method for determining a property of an arrangementwhich comprises an apparatus for microlithographic projection exposureand a substrate disposed in an exposure position of the apparatus. Theinvention further relates to an apparatus for inspecting a surface of asubstrate and to a method for determining a property of an arrangementwhich comprises this type of inspection apparatus and a substrate. Thesetypes of inspection apparatuses include microscopes and opticalinspection systems as used e.g. for the inspection of lithography masksor for the inspection of exposed wafers. Furthermore, they includeoptical systems for the calibration of mask patterning systems—so-called“registration units”—with which position marks can be measured withgreat precision on a lithography mask.

For the high precision imaging of micro- or nanostructures with the aidof a lithography exposure system it is important to know the positionand the topography or the surface properties of the substrate to beexposed, e.g., in the form of a so-called wafer. In order to establishthe position, focus sensors, for example, are used which, in directproximity to a substrate table, guide a measurement signal such that itpractically grazes the substrate plane and is then recaptured. In orderto measure the substrate topography, measuring optics set up in parallelto the projection optics are often also used. This type of measuringoptics is also called a “twin stage”. This type of measuring optics setup in parallel is associated with increased complexity becauseadditional optics and also an additional displacement stage arerequired.

With regard to the use of these types of metrology systems thedifficulty arises, in particular for lithography exposure systems whichare operated in the EUV wavelength range (wavelength range of extremeultraviolet radiation, e.g. 13.4 nm) that the working space of thesesystems on the substrate side is determined by the penultimate mirror inthe beam path. From the optical point of view, it is advantageous ifthis space can be chosen to be particularly small. However, a very smallworking space only leaves a small amount of or even no installationspace for a conventional focus sensor.

OBJECTS OF THE INVENTION

It is an object of the invention to provide an apparatus and a method ofthe type specified above with which the aforementioned problems areaddressed and/or resolved, and in particular with which a position ofthe substrate in relation to an imaging direction of the optical systemcan be determined with a smaller, or even the smallest possible, workingspace between the optical system and the substrate.

SUMMARY OF THE INVENTION

According to one formulation of the invention, an apparatus formicrolithographic projection exposure is provided which has an opticalsystem in the form of projection optics for imaging mask structures ontoa surface of a substrate by projecting the mask structures with imagingradiation. The optical system is configured to operate in the EUV and/orhigher frequency wavelength range, i.e. for wavelengths in the EUV rangeand/or for smaller wavelengths. This apparatus further has a measurementbeam path for guiding measurement radiation. The measurement beam pathextends within the optical system such that at least two opticalelements of the optical system are included in the measurement pathbeam, and the measurement radiation only partially passes through theoptical system during operation of the apparatus.

According to a further formulation of the invention, a method isprovided for determining a property of an arrangement which comprises anapparatus for microlithographic projection exposure and a substratedisposed in an exposure position of the apparatus. Here the apparatuscomprises an optical system for imaging mask structures onto the surfaceof the substrate by projecting the mask structures using imagingradiation in the EUV and/or higher frequency wavelength range. Themethod includes: guiding measurement radiation within the optical systemsuch that at least two optical elements of the optical system areincluded in the measurement path beam, and the measurement radiationonly partially passes through the optical system, and determining aproperty of the arrangement from the measurement radiation.

In other words, there is created within the optical system a beam pathfor measurement radiation with which a property of an arrangement whichcomprises the apparatus for microlithographic projection exposure and asubstrate disposed in an exposure position can be determined. Theoptical system serves to image mask structures onto a surface of asubstrate by projecting the mask structures with imaging radiation, andcan also be called a projection objective of the projection exposuresystem. The optical system is configured to operate with imagingradiation in the EUV and/or higher frequency wavelength range. The EUVwavelength range is identified as the range below 100 nm, in particularthe range between 5 nm and 20 nm. In particular, the optical system canbe configured to operate with a wavelength of 13.5 nm or 6.9 nm. Theconfiguration of the optical system to the aforementioned wavelengthrange generally requires the implementation of the optical system withpurely reflective optical elements, and so as a so-called catoptricprojection objective, and the provision of corresponding reflectivecoatings.

The measurement beam path extends within the optical system such that atleast two optical elements of the optical system are included in themeasurement beam path, and the measurement radiation only partiallypasses through the optical system during operation of the apparatus. Itis to be understood from this that not all of the optical elements areincluded in the measurement beam path. An optical element can, forexample, be included in the measurement beam path if the measurementradiation is reflected on the respective optical element. Another formof inclusion of an optical element in the form of a mirror on themeasurement beam path can consist of the measurement radiation passingthrough an opening in this mirror. In other words, the measurement beampath only extends in sections within the optical system, and so thereexists at least one optical element which is not included in themeasurement beam path in the sense specified above.

According to one exemplary embodiment, the position of the substratesurface for at least one point on the substrate surface is measured asregards the imaging direction. If the optical system has an opticalaxis, which is the case when using rotationally symmetrical opticalelements, the at least one point on the substrate surface is measured,in particular as regards its axial position, relative to the opticalaxis. The axial position is understood to be the position with regard toa coordinate axis which extends in the direction of the optical axis ofthe optical system.

The position of the substrate surface is then be determined byreflection of the measurement radiation on the substrate surface andsubsequent analysis of the reflected measurement radiation. Due to thefact that the measurement radiation radiates from within the opticalsystem onto the substrate surface, one can dispense with attachingmeasuring elements between the last element of the optical system andthe substrate. In this way the working space between the reflectiveoptical element lying closest to the substrate and the substrate can bekept very small. In the case where the measurement radiation is notreflected on the substrate, but rather e.g. on a mask having the maskpatterns, corresponding advantages with regard to the working spacebetween the reflective optical element lying closest to the mask and themask are achieved. These or similar effects can be achievedcorrespondingly if it is not the position on the substrate surface, butgenerally a property of the arrangement that is determined.

In one embodiment, the measurement beam path is configured to measure,during operation of the apparatus, at least one point of the substratesurface as regards its position with the measurement radiation guided bythe measurement beam path. In a further embodiment, the measurement beampath is configured to measure, during operation of the apparatus, the atleast one point of the substrate surface as regards its position in theimaging direction of the optical system with the measurement radiation.Furthermore, the apparatus preferably has an analysis device which isconfigured to determine the position of the point of the substratesurface from the measurement radiation after the latter interacts withthe substrate.

Generally, the apparatus according to one embodiment has an analysisdevice which is configured to determine a property of an arrangement ofthe measurement radiation and which includes the apparatus forprojection exposure and the substrate.

According to one embodiment the measurement beam path is configured suchthat the measurement radiation is reflected on a surface of thesubstrate during operation of the apparatus. In this case the axialposition on the substrate surface can then be determined from themeasurement radiation reflected on the substrate surface. This canhappen in different ways. For example, the measurement radiationreflected on the substrate surface can be determined with radiationmoved past the optical system and passing back to the same radiationsource as the measurement radiation, as described for example in US2007/0080281 A1. Furthermore, one can, for example, fall back on themeasuring principle described in U.S. Pat. No. 5,268,744 whereindisplacement of the substrate surface in the z direction brings aboutdisplacement of the measurement beam on a detector surface. A furthermeasuring principle of distance measurement is described in DE4109484C2.

In a further embodiment, the measurement beam path is configured tomeasure, during operation of the apparatus, the at least one point ofthe substrate surface as regards its position lateral to the imagingdirection of the optical system using the measurement radiation guidedby the measurement beam path. In this way the position of the at leastone point is measured in the lateral direction. This can happen inparticular with the aid of adjustment marks. In the simplest case justone adjustment mark, which is located on the substrate, is required.This adjustment mark is imaged onto a detector with the measurementradiation. The lateral position of the adjustment mark is taken from theposition of the imaged adjustment mark, and from this the lateralposition of the substrate, and so the so-called alignment of thesubstrate can be determined.

In addition to the adjustment mark on the substrate, a furtheradjustment mark can also be provided as a reference, e.g. on a referencemirror. This type of reference mark can be disposed upstream ordownstream of the substrate in the measurement beam path. In the case ofthe upstream positioning the measurement radiation strikes theadjustment mark on the substrate “pre-patterned”, and in the case of thedownstream positioning the measurement radiation patterned by thesubstrate mark is imaged onto the reference mark. In both cases animage, which includes the relative positions of the reference mark andthe substrate mark, can be recorded by a downstream detector. From thisthe lateral position of the substrate mark relative to the referencemark can be determined. An example of this type of positiondetermination using substrate and reference marks is the Moiré method.The Moiré measuring method, known in principle to the person skilled inthe art, utilises the Moiré effect with which long-period brightnessmodulations are generated by overlaying two line grids the gridconstants of which deviate only slightly from one another. By analysingthe pattern produced, a relative displacement of the two grids inrelation to one another can be determined with a high degree ofprecision. The Moiré analysis is advantageously implemented with thetwo-dimensional intensity pattern determined with the spatiallyresolving surface sensor.

For apparatuses for microlithographic projection exposure, in particularfor methods which require high-precision lateral overlay of structures,and so have high “overlay” requirements, as is the case e.g. withdouble-patterning methods, this type of lateral position measurement isimportant. A measurement of the lateral position is also relevant to theinspection apparatuses described below. For these types of apparatus,also called “registration units”, it is made possible to take a lateralposition measurement, e.g. for a so-called “pre-alignment”, i.e. a typeof rough positioning. In one embodiment the high-precision measurementof the adjustment marks is then not implemented using the measurementbeam path, but a different beam path, e.g. the imaging beam path.

In a further embodiment, the apparatus for microlithographic projectionexposure has a substrate table displaceable laterally to the imagingdirection and a control device. The control device is configured tocontrol the apparatus such that during operation of the apparatus the atleast one point of the substrate surface is measured at two differentpoints in time as regards its position lateral to the imaging direction,and the apparatus is set up to determine from this a lateraldisplacement speed or a so-called “scan speed” of the substrate table.The substrate is held by the substrate table which can also be calledthe “wafer stage”.

In a further embodiment, the measurement beam path is configured suchthat during operation of the apparatus the measurement radiation isreflected on a surface of the substrate.

In a further embodiment, the apparatus has a measurement radiationsource which generates the measurement radiation with at least twodifferent wavelengths. Furthermore, the apparatus comprises awavelength-resolving radiation detector which is configured to measurethe respective intensity of the measurement radiation followingreflection on the substrate for each of the at least two differentwavelengths, and to determine from this the temperature on the substratesurface. This takes place in the same way as temperature determinationwith an infrared thermometer.

In a further embodiment, the mask structures to be imaged are disposedon a mask, and the measurement beam path is configured such that duringoperation of the apparatus the measurement radiation is reflected on asurface of the mask facing towards the optical system.

In a further embodiment, the apparatus comprises a mask table that canbe displaced laterally to the imaging direction and a control devicewhich is configured to control the apparatus for microlithographicprojection exposure such that during operation of the apparatus the atleast one point of the substrate surface is measured as regards itsposition lateral to the imaging direction at two different points intime, the apparatus being set up to determine from this a lateraldisplacement speed of the mask table.

In a further embodiment, the apparatus comprises a measurement radiationsource which generates the measurement radiation with at least twodifferent wavelengths. Furthermore, the apparatus includes awavelength-resolving radiation detector which is configured to measurethe respective intensity of the measurement radiation followingreflection on the mask surface for the at least two differentwavelengths, and from this to determine the temperature on the substratesurface.

In a further embodiment, the apparatus is configured to determine,during operation of the apparatus, a reduction in intensity of themeasurement radiation upon passing through the optical system, and todetermine from this a concentration of a gas contained in the opticalsystem. This gas surrounds the optical elements of the optical system.This can also be a residual gas of an optical system operated in avacuum.

In a further embodiment, the apparatus further comprises an opticalinjecting element which is provided for injecting the measurementradiation into the optical system. Moreover, an optical extractingelement, which is provided for extracting the measurement radiation fromthe optical system, can be provided. For this purpose two deflectionmirrors can be provided which are configured to reflect the measurementradiation. The deflection mirrors are advantageously independent of theat least one reflective optical element of the optical system. In oneembodiment the first deflection mirror is positioned such that it steersthe measurement radiation onto one of the reflective optical elementsor, in the embodiment in which one of the reflective optical elementshas an opening, onto this opening.

In a further embodiment, the measurement beam path is configured suchthat, during operation of the apparatus, the measurement radiation isreflected on the surface of the substrate or the surface of the maskbetween injection into the optical system and extraction from theoptical system. In this way it is possible to determine an axialposition of the substrate on the reflection point relative to theoptical system.

In a further embodiment, the optical system has at least one reflectiveoptical element, and the measurement beam path extends within theoptical system such that during operation of the apparatus themeasurement radiation is reflected on the at least one reflectiveoptical element. According to a further variation the measurement beampath extends within the optical system such that during operation of theapparatus the measurement radiation passes through an opening in the atleast one reflective optical element.

In a further embodiment, the apparatus further comprises a substrateplane into which the mask structures are imaged during operation of theapparatus, the measurement beam path being configured such that themeasurement radiation is focussed onto the substrate plane.

In a further embodiment, an obscuration aperture is disposed in a pupilplane of the optical system. This type of obscuration aperture is alsocalled a shading aperture. This can be created, for example, using anon-reflective coating with regard to radiation with the wavelength ofthe imaging radiation. This type of obscuration aperture is often usedto avoid a high degree of light loss in the beam path of the imagingradiation because in an obscured system smaller angles of incidence canbe achieved, as described, for example, in WO 2006/069725 A1. Anobscuration aperture often blocks the imaging radiation in a centralregion of the beam cross-section. By positioning an obscuration aperturein a pupil plane area-independent obscuration of the pupil can beachieved. This type of optical system with an obscured pupil benefitsparticularly in the context of the invention because the size of theobscuration can be smaller the smaller the working space between theoptical system and the substrate.

In a further embodiment, the at least one reflective optical element hasan opening, and the measurement beam path extends through this opening.The at least one reflective optical element having the opening isdownstream in relation to the obscuration aperture in the beam path ofthe imaging radiation, the opening being disposed in a region of thereflective optical element which is at least partially shaded from theimaging radiation by the obscuration aperture. Therefore, the imagingcharacteristics of the optical system are not negatively effected by themeasurement radiation.

In a further embodiment, an obscuration aperture is disposed in a firstpupil plane, the optical system has a further pupil plane downstream inrelation to the obscuration aperture in the imaging beam path which isshaded in some regions by the obscuration aperture, and the measurementbeam path extends at least once through the further pupil plane, atleast partially in the shaded region. The further pupil plane can bedisposed, for example, between the penultimate and the last reflectiveoptical element of the optical system before the substrate. Preferablythe measurement radiation passes through the further pupil plane twice.

In a further embodiment, the measurement beam path extends at least oncethrough a pupil plane of the optical system.

In a further embodiment, at least one of the reflective optical elementshas an opening, and the measurement beam path extends through thisopening. In this embodiment the opening is disposed in a central regionof the at least one reflective optical element. By positioning theopening in the central region of the reflective optical element, theopening has, if it has any effect at all, a symmetrical effect upon theimaging beam path in the optical system. In this way imaging errors whenimaging the mask structures with the optical system are avoided.

In a further embodiment, the optical system comprises at least tworeflective optical elements, and the measurement beam path extendsthrough both openings. In one embodiment the reflective optical elementshaving the respective openings are disposed in a high-aperture part ofthe optical system, in particular these are the last two reflectiveoptical elements of the optical system.

In a further embodiment, the at least one reflective optical element hasan opening, and the measurement beam path is configured such that duringoperation of the apparatus the measurement radiation passes through theopening and is reflected on at least one other reflective opticalelement of the optical system. In this way, aspects and benefitsassociated with the invention can be realised through a variety ofoptical designs for the optical system.

In a further embodiment, the measurement beam path is configured suchthat during operation of the apparatus the measurement radiation isreflected on the at least one reflective optical element, the latterhaving a peripheral region disposed outside of the beam path of theimaging radiation, and the measurement beam path being configured suchthat the measurement radiation is reflected on the peripheral region.This peripheral region can, for example, have a reflective coatingmatched especially to the wavelength of the measurement radiation.Therefore, greatly differing wavelengths can be used for the imagingradiation and the measurement radiation.

In a further embodiment, the measurement beam path is configured suchthat the measurement radiation is reflected twice on the at least onereflective optical element. Preferably the measurement radiation isreflected once prior to reflection on the substrate, and once after thison the respective reflective optical element. Therefore, the measurementradiation reflected on the substrate can also be guided through theinterior of the optical system to a detector device so that no furtheroptical element need be disposed between the last optical element andthe substrate plane. Therefore, the working space of the optical systemcan remain unaffected by the detection of the measurement radiation.

In a further embodiment, the optical system comprises a number ofoptical elements, and the measurement beam path is configured such thatduring operation of the apparatus the measurement radiation is reflectedon at least two, in particular on three, four, five, six, etc. of thereflective optical elements. In one embodiment the reflection on thereflective optical elements takes place before the measurement radiationstrikes the substrate, and then the measurement radiation is reflectedonce again on said reflective optical elements.

In a further embodiment, none of the reflective optical elements of theoptical system has an opening in the optically used region of an opticalarea. Therefore, the optical areas of the reflective optical elementsare all designed to be continuous. Therefore, within the optical systemthe measurement radiation is either reflected on a respective reflectiveoptical element or runs past it.

In a further embodiment, the measurement beam path is configured suchthat the relative position of at least two points on the surface of thesubstrate, in particular the topography of at least one section of thesurface of the substrate, can be measured with the measurement radiationguided therein. In other words, a number of points on the surface of thesubstrate are measured as regards their relative axial position inrelation to one another with the measurement radiation. From this thesurface properties of the substrate surface can be determined. From thesurface properties determined matching of the exposure conditions withregard to the focus setting for the imaging of the mask structures ontothe substrate surface can in turn take place.

In a further embodiment, at a given time during operation of theapparatus a limited area on the substrate is exposed with the imagingradiation, and the measurement beam path is configured such that at thetime of exposing the substrate the measurement radiation is directedonto the exposed area. Therefore, the position measurement on thesurface of the substrate takes place simultaneously during exposure ofthe respective substrate area. Any possible errors in the positioncaused by a scanning movement of the substrate can be eliminated by thesimultaneous measurement. The exposed area on the substrate at any giventime can in the case of a projection exposure system in the form of aso-called stepper be e.g. the whole exposed field on the wafer, or inthe case of a projection exposure system in the form of a so-calledscanner, be a slot-shaped area illuminated by the exposure slot.

In a further embodiment, the apparatus is configured as a scannerwherein during operation a slot-shaped area on the substrate is exposedby an exposure beam, the substrate being moved relative to the exposurebeam so that the exposed area is displaced on the substrate. In thisembodiment the measurement beam path is configured such that themeasurement radiation is directed towards a section of the substratewhich during exposure operation of the exposed area runs ahead and/orruns behind. In the case where the measurement radiation is directedtowards the section running ahead of the exposed area there is theadvantage that prior to exposure of the section of the substrate“sampled” in advance using the measurement radiation, the focus settingsrequired for exposure are already provided. Therefore, there issufficient lead time in order to establish an optimal focus setting, forexample by mechanical manipulations, for the exposure of the substratesection. In the case of “subsequent measurement” of the substratesurface the measurement result can serve, for example, to verify theimaging settings in retrospect or also for quality control of theexposure.

In a further embodiment, the apparatus is configured to determine theposition of the at least one point of the substrate surface while at thesame time imaging the mask structures onto the substrate surface. Inthis case the measurement of the substrate surface during the exposureoperation takes place in real time.

According to another aspect of the invention, furthermore, an apparatusfor microlithographic projection exposure is provided comprising: anoptical system for imaging mask structures onto a surface of a substrateby projecting the mask structures in an imaging direction with imagingradiation, the optical system having at least one reflective opticalelement and a measurement beam path for guiding measurement radiation,the measurement radiation serving to measure at least one point of thesubstrate surface as regards its position in the projection direction,and the measurement beam path being configured such that duringoperation of the apparatus the measurement radiation is reflected on atleast one of the reflective optical elements.

Moreover, an apparatus for microlithographic projection exposure isprovided comprising: an optical system for imaging mask structures ontoa surface of a substrate by projecting the mask structures with imagingradiation, the optical system having at least one reflective opticalelement. Furthermore, the optical system comprises a measurement beampath for guiding measurement radiation, the measurement beam pathextending, in particular in sections, within the optical system suchthat during operation of the apparatus the measurement radiation isreflected on the at least one reflective optical element and,furthermore, on the surface of the substrate.

The reflective optical element is in particular an optical elementgenerating the imaging beam path. In other words, in this case thereflective optical element is positioned within the optical system suchthat it reflects the imaging radiation onto the surface of the substratewhen imaging the mask structures. It is therefore an imaging opticalelement of the optical system with regard to the imaging of the maskstructures.

Moreover, an apparatus for microlithographic projection exposure isprovided. This apparatus comprises: an optical system for imaging maskstructures onto a surface of a substrate by projecting the maskstructures with imaging radiation, the optical system having at leastone reflective optical element. Furthermore, the apparatus comprises ameasurement beam path for guiding measurement radiation, the measurementbeam path extending, at least in sections, within the optical systemsuch that during operation of the apparatus the measurement radiationpasses through an opening in the at least one reflective optical elementand, furthermore, is reflected on the surface of the substrate. In thepresent case the optical system can be configured as a catadioptricsystem which, in addition to the at least one reflective opticalelement, comprises at least one refractive or diffractive opticalelement, but also as a catoptric system.

Furthermore, according to another aspect of the invention, a method isprovided for determining a property of an arrangement which comprises anapparatus for microlithographic projection exposure and a substratedisposed in an exposure position of the apparatus. The apparatuscomprises an optical system for imaging mask structures onto the surfaceof the substrate by projecting the mask structures in an imagingdirection using imaging radiation. The optical system has at least onereflective optical element, and the method comprises the steps: guidingmeasurement radiation within the optical system such that themeasurement radiation is reflected on the at least one reflectiveoptical element or passes through an opening in the at least one of thereflective optical elements, reflecting the measurement radiation on thesurface of the substrate, and determining a property of the arrangementfrom the reflected measurement radiation.

Moreover, an apparatus for microlithographic projection exposure isprovided which comprises: an optical system for imaging mask structuresonto a surface of a substrate by projecting the mask structures in animaging direction with imaging radiation, the optical system having atleast one reflective optical element. The apparatus further comprises ameasurement beam path for guiding measurement radiation, which serves tomeasure at least one point of the substrate surface as regards itsposition in the imaging direction. Here at least one of the reflectiveoptical elements has an opening, and the measurement beam path extendsthrough this opening.

Furthermore, a method is provided for determining a position on asurface of a substrate which is disposed in an exposure position in anapparatus for microlithographic projection exposure. The apparatus hasan optical system here for imaging mask structures onto the surface ofthe substrate by projecting the mask structures using imaging radiation.The optical system has at least one reflective optical element, and themethod according to one formulation, comprises: guiding measurementradiation, in sections, within the optical system such that themeasurement radiation is reflected on the at least one reflectiveoptical element or passes through an opening in the at least onereflective optical element, reflecting the measurement radiation on atleast one point on the surface of the substrate, and determining aposition of the at least one point of the substrate surface relative tothe imaging direction from the reflected measurement radiation.Preferably said opening in the reflective optical element is designedsuch that the imaging of the mask structures onto the surface of thesubstrate is not or is only slightly affected by the imaging radiationthrough the opening. In the case where the optical system has apartially obscured pupil, the opening can be positioned in an obscuredregion of the imaging beam path.

As already mentioned above, the apparatus can be configured as aprojection exposure system for microlithography, in particular as an EUVprojection exposure system.

Furthermore, according to yet another formulation of the invention, anapparatus for inspecting a surface of a substrate is providedcomprising: an optical system for imaging at least one section of asurface of a substrate to be inspected into a detection plane by imagingthe section with imaging radiation, the optical system having at leastone reflective optical element, and a measurement beam path for guidingmeasurement radiation, the measurement beam path extending, in sections,within the optical system such that during operation of the apparatusthe measurement radiation is reflected on the reflective optical elementor passes through an opening in the reflective optical element.

Moreover, according to a further formulation of the invention, anapparatus for inspecting a surface of a substrate is providedcomprising: an optical system for imaging at least one section of asurface of a substrate to be inspected into a detection plane by imagingthe section in an imaging direction with imaging radiation, the opticalsystem being configured to operate in the EUV and/or higher frequencywavelength range, and a measurement beam path for guiding measurementradiation, the measurement beam path extending within the optical systemsuch that the measurement radiation only partially passes through theoptical system during operation of the apparatus. Therefore, thesubstrate can be a semiconductor wafer, a lithography mask or in generalan object to be inspected.

Moreover, a method for determining a property of an arrangement isprovided which comprises an inspection apparatus and a substrate whichis disposed in an inspection position in the inspection apparatus, theapparatus having an optical system for imaging at least one section of asurface of the substrate to be inspected into a detection plane byimaging the section using imaging radiation in the EUV and/or higherfrequency wavelength range, the optical system comprising at least onereflective optical element, and the method comprising the steps: guidingmeasurement radiation within the optical system such that themeasurement radiation only partially passes through the optical system,and determining a property of the arrangement from the measurementradiation.

Moreover, an apparatus for inspecting a surface of a substrate isprovided comprising: an optical system for imaging at least one sectionof a surface of a substrate to be inspected into a detection plane byimaging the section in an imaging direction with imaging radiation, theoptical system having at least one reflective optical element and ameasurement beam path for guiding measurement radiation, the measurementbeam path extending, in particular in sections, within the opticalsystem such that during operation of the apparatus the measurementradiation is reflected on the at least one reflective optical element,or passes through an opening in the at least one reflective opticalelement.

According to one embodiment of this inspection apparatus, the latter hasan analysis device which is configured to determine a property of anarrangement comprising the apparatus for projection exposure and thesubstrate from the measurement radiation. This type of property that canbe determined with the analysis device can be e.g. the position of apoint of the substrate surface.

Moreover, a method for determining a property of an arrangement isprovided which comprises an inspection apparatus and a substrate whichis disposed in an inspection position in the inspection apparatus, theapparatus having an optical system for imaging at least one section of asurface of the substrate to be inspected into a detection plane byimaging the section using imaging radiation, the optical system havingat least one reflective optical element, and the method comprising thesteps: guiding measurement radiation within the optical system such thatthe measurement radiation is reflected on the at least one reflectiveoptical element, or passes through an opening in the at least onereflective optical element, reflecting the measurement radiation on thesurface of the substrate, and determining a property of the arrangementfrom the reflected measurement radiation.

Moreover, according to a further aspect of the invention, a method isprovided for determining a position on a surface of a substrate which isdisposed in an inspection position in an inspection apparatus, theapparatus having an optical system for imaging at least a section of asurface of the substrate to be inspected into a detection plane byimaging the section in an imaging direction using imaging radiation, theoptical system having at least one reflective optical element, and themethod comprising: guiding measurement radiation, in sections, withinthe optical system such that the measurement radiation is reflected onthe at least one reflective optical element, or passes through anopening in the at least one of the reflective optical elements,reflecting the measurement radiation on at least one point on thesurface of the substrate, and determining a position of the at least onepoint of the substrate surface relative to the imaging direction fromthe reflected measurement radiation.

According to one embodiment, the inspection apparatus is configured as amicroscope. In a further embodiment, the inspection apparatus isconfigured as an optical inspection system for inspecting substratesexposed by a microlithographic projection exposure system. Moreover, ina further embodiment the apparatus is in the form of an opticalinspection system for inspecting masks for microlithography. Therefore,the inspection apparatus can be configured to calibrate mask structuringsystems, and so as a so-called “registration unit” wherein positionmarks on a lithography mask are measured with great precision. From thismeasurement conclusions can be drawn regarding the writing accuracy ofmask structures disposed on the lithography mask and which are intendedfor imaging onto a wafer.

The features specified in relation to the embodiments of the apparatusfor microlithographic projection exposure listed above can be appliedcorrespondingly to the apparatus for inspecting a surface of asubstrate.

Furthermore, the features specified in relation to the embodiments ofthe apparatus summarized above can be applied correspondingly to themethods summarized, and vice versa. The resulting embodiments of themethod are therefore hereby incorporated by this reference into thepresent disclosure. Furthermore, the aspects and advantages summarizedabove in relation to the embodiments of the apparatus therefore alsoapply to the corresponding embodiments of the method and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, exemplary embodiments of an apparatus according to theinvention for microlithographic projection exposure are discussed ingreater detail with reference to the attached schematic drawings. Theseshow as follows:

FIG. 1 a schematic side view of a first embodiment of an apparatus formicrolithographic projection exposure in a first illustration plane witha greatly schematically illustrated imaging beam path and a measurementbeam path,

FIG. 2 a detailed illustration of the imaging beam path according toFIG. 1,

FIG. 3 the imaging beam path in the schematised illustration accordingto FIG. 1 with an individual beam serving to illustrate the precisecourse of the beam,

FIG. 4 a sectional view of the imaging beam path according to FIGS. 1 to3 in a second illustration plane rotated by 90°,

FIG. 5 a top view of a reflective optical element of the apparatus formicrolithographic projection exposure,

FIG. 6 a sectional view of a second embodiment of the apparatus formicrolithographic projection exposure in the first illustration plane,

FIG. 7 a sectional view of a third embodiment of the apparatus formicrolithographic projection exposure in the first illustration plane,with which only the imaging beam path is drawn in,

FIG. 8 the apparatus according to FIG. 7, with which only onemeasurement beam path is drawn in,

FIG. 9 the imaging beam path according to FIG. 7 in the secondillustration plane,

FIG. 10 a top view of a substrate exposed by one of the apparatusesillustrated above in order to illustrate the exposure process,

FIG. 11 a sectional view of a further embodiment of the apparatus formicrolithographic projection exposure in the first illustration planewith which only one measurement beam path is drawn in, and

FIG. 12 a sectional view of an embodiment of an apparatus for inspectinga surface of a substrate.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the exemplary embodiments described below any elements which arefunctionally or structurally similar to one another are provided as faras possible with the same or similar reference numbers. Therefore, inorder to understand the features of the individual elements of aspecific exemplary embodiment, reference should be made to thedescription of other exemplary embodiments or to the more generaldescription of the invention.

FIG. 1 shows a first embodiment of an apparatus 10 for microlithographicprojection exposure in the form of an EUV projection exposure system ina sectional view in the x-z plane according to the coordinate systemdrawn in in the figure. As shown in the drawing, the apparatus 10 can bedesigned as a so-called step and scan exposure system, called “scanner”for short, or also as a so-called “stepper”.

The apparatus 10 comprises an illumination system 12 which radiatesillumination radiation 13 in the EUV wavelength range (extremeultraviolet radiation, e.g. with a wavelength of 13.4 nm) onto a mask 14with mask patterns 16 positioned over the latter. The mask 14 is held bya mask table 11 in the form of a so-called “reticle stage”.

The apparatus 10 further comprises an optical system 18 in the form ofprojection optics for imaging the mask structures 16 onto a surface 21of a substrate 20 in the form of a wafer disposed in a substrate plane19. The apparatus 10 further comprises a substrate table 20 a in theform of a so-called “wafer stage” by which the substrate 20 is held. Asalready mentioned above, according to the embodiment shown the apparatusis configured as a so-called “scanner”. During the exposure of an areaon the substrate 20, both the mask table 11 and the substrate table 20 aare displaced at different speeds in the y direction according to thecoordinate system shown in FIG. 1.

The optical system 18 comprises purely reflective optical elements 22 inthe form of mirrors. Therefore, the optical system 18 can also be calleda catoptric projection objective. The imaging of the mask structures 16onto the surface 21 of the substrate 20 is implemented by projecting themask patterns in an imaging direction 17 a. The imaging direction 17 aextends in the direction of a reference axis 17 of the optical system18, which according to FIG. 1 extends in the z direction. In the casewhere reflective optical elements 22 are rotationally symmetric, thereference axis 17 corresponds to the optical axis of the optical system.

The illumination radiation 13 is transformed by the mask 14 into imagingradiation 15. The imaging radiation 15 passes through the imaging beampath 24 in the optical system 18 which is shown as an outline in FIG. 1in order to provide a clearer illustration. FIG. 2 shows the imagingbeam path 24 with a plurality of individual beams contained therein. Asa further illustration of the path of the imaging radiation 15 in theoptical system 18 an exemplary individual beam 25 of the imagingradiation 15 is shown in FIG. 3. As is evident from this, the imagingradiation 15 is reflected on the individual reflective optical elements22-1 to 22-6, one after the other, in the imaging beam path 24. Here theelements 22-1 and 22-2 are respectively a concave mirror, element 22-3is a convex mirror, element 22-4 is once again a concave mirror, element22-5 is a convex mirror, and element 22-6 is in turn a concave mirror.

The optical system 18 has a first pupil plane 28 disposed between thereflective optical elements 22-3 and 22-4. Disposed in the first pupilplane 28 there is in a central region of the beam cross-section of theimaging radiation 15 an obscuration aperture 29, also called a shadingaperture. The obscuration aperture 29 brings about area-dependentobscuration of the pupil, and is made of a material, or has a coating,which does not reflect any radiation with the exposure wavelength in theEUV wavelength range. The material substantially absorbs the incomingradiation with this wavelength.

The reflective optical elements 22-5 and 22-6 downstream in the beampath 24 are disposed in a high aperture part of the optical system 18,and each have an opening 26 in the form of a central hole through therespective reflective optical surface 27. FIG. 5 shows this type ofopening 26 in an exemplary reflective optical element 22. As shown inFIG. 5, the opening 26 can be in the shape of a circular disc or alsohave other forms. The opening 26 is disposed in a region of thereflective optical elements 22-5 and 22-6 which is at least partiallyshaded by the obscuration aperture 29. This type of obscuration aperture29 can serve to prevent a high degree of light loss in the illuminationbeam path 24, as described, for example, in WO 2006/069725.

Furthermore, the apparatus 10 has a measurement radiation source 32 forgenerating measurement radiation 34. The measurement radiation 34 canhave a different wavelength than the imaging radiation 15, e.g. awavelength in the visible wavelength range, in particular e.g. 632.8 nm,in the UV wavelength range, in particular the DUV wavelength range, e.g.248 nm, the VUV wavelength range, e.g. 193 nm, or also in the infraredrange. The measurement radiation 34 is injected into the optical system18 by a first deflection mirror 38 in the form of an injecting mirror orinjecting element. The injection takes place such that the measurementbeam path 36 initially passes through the opening 26 in the reflectiveoptical element 22-6 and then through the opening 26 in the reflectiveoptical element 22-5.

The measurement radiation 34 is then reflected on the surface 21 of thesubstrate 20 and passes through the openings 26 in the optical elements22-5 and 22-6 once again. Here the measurement beam path 36 passes twicethrough a second pupil plane 30 conjugated to the first pupil plane 28in a region shaded by the obscuration aperture 29. After passing throughthe openings 26 in the elements 22-5 and 22-6 once again, themeasurement radiation 34 is steered by a second deflection mirror 40 inthe form of an extracting mirror or extracting element onto a detectorsystem 42. Since the measurement radiation 34 neither passes through noris reflected on a series of optical elements of the optical system 18,in particular the optical elements 22-1 and 22-2, the measurementradiation 34 only partially passes through the optical system 18.

Using the detector system 42, the point or a number of points on thesubstrate surface 21 at which the measurement radiation 34 was reflectedis/are measured as regards its/their position in the imaging direction17 a. For this purpose the detector system 42 comprises a detector andan analysis device 45 which determines the axial position of the pointor the points on the substrate surface 21 to be measured from the signalrecorded by the detector. Since the imaging direction 17 a according toFIG. 1 extends parallel to the z coordinate axis, the z coordinate ofthe point or the respective z coordinates of a number of points is/aredetermined. This can happen, for example, by overlaying the reflectedmeasurement radiation 34 with radiation from the measurement radiationsource 32 moved past the optical system 18, as described, for example,in US 2007/0080281 A1. Alternatively, the measuring principle describedin U.S. Pat. No. 5,268,744 can be used with which the displacement ofthe substrate surface 21 in the z direction also leads to a displacementof the striking location of the measurement radiation on a detectorsurface in the detector system 42. Alternatively, the measuring systemdescribed in DE 4109484 C2 can also be used to analyse the reflectedmeasurement radiation 34. FIG. 4 shows the imaging beam path 24according to FIGS. 1 to 3 in the y-z plane. Using the measurementradiation 34, the topography of the substrate surface 21, and so therelative position of a number of points on the substrate surface 21 inrelation to one another, can also be determined.

Furthermore, the measurement radiation 34 can also be used to determinethe lateral position of an adjustment mark disposed on the substratesurface 21, and so be used for the alignment of the substrate 20 beforeit is exposed. As already explained in greater detail above, for thispurpose the adjustment mark can be imaged directly onto the detectorsystem 42. Alternatively, in addition a reference mark can be disposedin the measurement beam path 36, for example on a reference mirror. Onepossibility for determining the lateral position is the Moiré measuringmethod known in principle to the person skilled in the art.

FIG. 6 shows the apparatus 10 in sections in a second embodiment in asectional view in the x-z plane. The apparatus 10 according to FIG. 6differs from the apparatus 10 according to FIG. 1 only in theconfiguration of the measurement beam path 36. The measurement beam path36 according to FIG. 6 is configured such that after injection into theoptical system 18 the measurement radiation 34 is initially reflected bythe first deflection mirror 38 on the reflective optical element 22-6.The reflection takes place here on a peripheral region 23 of thereflective optical element 22-6. This peripheral region 23 can bedisposed outside or inside the imaging beam path 15, and it can alsopartially overlap with the imaging beam path 15.

The measurement radiation 34 reflected on the peripheral region 23 thenpasses through the opening 26 in the reflective element 22-5, isreflected on the substrate surface 21, passes through the opening 26 inthe reflective element 22-5 once again, and is then reflected again onthe peripheral region 23 of the reflective element 22-6. The repeatedreflection takes place on an opposing region of the peripheral region 23with regard to the first reflection relative to the reference axis 17 ofthe optical system 18. The measurement radiation 34 is then steered bythe second deflection mirror 40 onto the detector system 42.

FIGS. 7 to 9 show a third embodiment of an apparatus 10 formicrolithographic projection exposure. In order to provide a betterillustration, in FIGS. 7 and 9 respectively only the imaging beam path24, and in FIG. 8 only the measurement beam path 36 is shown. FIGS. 7and 8 show the embodiment in a sectional view in the x-z plane, and FIG.9 in a sectional view in the y-z plane.

Unlike the previously described optical systems 18, the optical system18 according to FIGS. 7 to 9 does not have an obscuration aperture 29.As is evident from FIG. 9, the imaging radiation 15 is guided past theside of individual respective optical elements 22-1 to 22-6 before orafter reflection on the optical elements in question without penetratinga reflective optical surface. Therefore, unlike the previousembodiments, the reflective optical elements 22-1 to 22-6 do not have anopening 26.

As shown by FIG. 8, the measurement beam path 36 also extends such thatthe measurement radiation 34 is either reflected on the reflectiveoptical elements 22-1 to 22-6 or runs past them. Therefore, in thisembodiment the measurement radiation 34 does not pass through an openingin a reflective optical element 22. Following injection into the opticalsystem 18 via the first deflection mirror 38, the measurement radiation34 is reflected, one after the other, on the reflective optical elements22-3 in the form of a convex mirror, 22-4 also in the form of a convexmirror, 22-5 also in the form of a convex mirror, and 22-6, which isalso in the form of a convex mirror. The measurement radiation 34 thenpasses onto the substrate surface 21 and passes through the opticalsystem 18 by reflection on the aforementioned elements in the oppositesequence before it is steered onto the detector system 42 by the seconddeflection mirror 40.

FIG. 10 shows a top view of the substrate 20 in the form of a wafer withan area 43 to be exposed drawn in as an example. In the case where theapparatus 10 is designed as a “scanner”, the exposure beam radiatingonto the substrate is formed such that the latter exposes a slot-shapedarea 44 at a given point in time. This slot-shaped area can berectangular or also in the shape of a ring segment. During scanoperation the substrate 20 is scanned in the y direction 50 relative tothe fixed optical system 18. The effect of this is that the slot-shapedexposed area 44 is effectively scanned in the opposite direction 52.

In all of the embodiments of the apparatus 10 described above, themeasurement beam path 36 can be configured in three differentvariations. In a first variation the measurement radiation 34 isdirected towards a point or a region within the slot-shaped exposed area44 at the time when it is exposed. Therefore, a simultaneous measurementof the surface properties of the substrate surface 21 is taken duringthe scanning process. In a second variation, the measurement radiation34 is directed at a section 46 of the substrate 20 running ahead of theexposed area 44. In a third variation the measurement radiation 34 is,in contrast, directed at section 48 of the substrate 20 running behindthe exposed area 44.

In a further embodiment of the apparatus 10, a point on the substratesurface 21 is measured, as regards its position lateral to the imagingdirection 17 a, at two different times during the scanning movement ofthe substrate 20. From this the scanning speed and the lateraldisplacement speed of the substrate 20 is determined.

In a further embodiment, of the apparatus 10, the measurement radiation34 generated by the measurement radiation source 32 has at least twodifferent wavelengths. The radiation detector 42 is wavelength-resolvingand determines the respective intensity of the measurement radiation 34following reflection on the substrate surface 21 for the at least twodifferent wavelengths. From the radiation intensities the temperature ofthe substrate surface 21 is then determined in the same way as with thefunction of an infrared thermometer.

In a further embodiment of the apparatus 10, during operation of theapparatus 10, a reduction in intensity of the measurement radiation 34upon passing through the optical system 18 is determined, and from thisa concentration of a gas contained in the optical system 18 isdetermined.

FIG. 11 shows a further embodiment of the apparatus 10 formicrolithographic projection exposure. With this embodiment, themeasurement beam path 36 is formed such that during operation of theapparatus 10 the measurement radiation 34 is reflected on a surface 14 aof the mask 14 facing towards the optical system 18. Therefore, forexample, the position of a point of the mask surface 14 a or also thetopography of the mask surface 14 a can be determined. Also, otherproperties of the apparatus specified above with regard to theembodiment with which the measurement radiation 34 is reflected on thesubstrate 20 can be determined.

FIG. 12 shows an embodiment of an apparatus 110 for inspecting a surfaceof a substrate 20. This can be a microscope or an optical inspectionsystem, e.g. for the inspection of lithography masks or for theinspection of exposed wafers. The apparatus can also be configured tocalibrate mask shaping systems, and so as a so-called “registrationunit” with which position marks on a lithography mask are measured withhigh precision. From this measurement conclusions can be drawn regardingthe writing precision of mask structures disposed on the lithographymask and intended to image into a wafer.

The substrate 20 can therefore be a semiconductor wafer, a lithographymask or generally an object to be inspected. The apparatus 110 onlydiffers from the previously described apparatuses 10 formicrolithographic projection exposure in that the imaging takes place inthe opposite imaging direction 17 a. The substrate 20 is illuminated byillumination radiation 113 radiated at an angle. The imaging radiation15 remitted from the surface 21 of the substrate 20 passes through theimaging beam path 24 of the optical system 18 in the opposite directionin comparison to the apparatus 10. A section of the surface 21 to beinspected is imaged onto a detection surface 158 of a detection device154 disposed in a detection plane 156 and is thereby detected.

The apparatus 110 comprises a measurement beam path 36 formed in thesame way as the measurement beam path 36 according to FIG. 1. Theembodiments shown in FIGS. 2 to 5 can be correspondingly applied to theapparatus 110 in the embodiment according to FIG. 12. Furthermore, theapparatus 110 can be realized in further embodiments similar to theapparatuses 110 according to FIGS. 6 to 9.

The above description of the preferred embodiments has been given by wayof example. From the disclosure given, those skilled in the art will notonly understand the present invention and its attendant advantages, butwill also find apparent various changes and modifications to thestructures and methods disclosed. The applicant seeks, therefore, tocover all such changes and modifications as fall within the spirit andscope of the invention, as defined by the appended claims, andequivalents thereof.

The invention claimed is:
 1. An apparatus for microlithographicprojection exposure comprising: an optical system comprising a pluralityof optical elements and configured to image mask structures onto asurface of a substrate by projecting the mask structures with anexposure beam of imaging radiation having an extreme ultraviolet orshorter wavelength onto an exposure area of the substrate surface,wherein the optical system is a catoptric system, and structure defininga measurement beam path and configured to guide measurement radiation,the measurement beam path extending within the optical system such thatthe measurement radiation impinges onto a measurement area of thesubstrate surface, wherein the apparatus is configured as a scanner,wherein during an exposure operation performed by the apparatus, theexposure area on the substrate surface is exposed by the exposure beamwhile the substrate is moved relative to the exposure beam in a scanningdirection, thereby displacing the exposure area on the substratesurface, and wherein the measurement beam path is configured such thatthe measurement area moves, offset from the exposure area, on thesubstrate surface during the exposure operation.
 2. The apparatusaccording to claim 1, wherein the substrate is moved relative to theexposure beam in a predetermined scanning direction and wherein themeasurement area is offset upstream from the exposure area in thescanning direction during the exposure operation.
 3. The apparatusaccording to claim 1, wherein the substrate is moved relative to theexposure beam in a predetermined scanning direction and wherein themeasurement area is offset downstream from the exposure area in thescanning direction during the exposure operation.
 4. The apparatusaccording to claim 1, wherein the measurement beam path extends withinthe optical system such that at least two of the optical elements of theoptical system are included in the measurement beam path.
 5. Theapparatus according to claim 1, which is configured to determine aposition of at least one point of the substrate surface during theexposure operation.
 6. The apparatus according to claim 1, furthercomprising an optical injecting element configured to inject themeasurement radiation into the optical system.
 7. The apparatusaccording to claim 1, further comprising an optical extracting elementconfigured to extract the measurement radiation from the optical system.8. The apparatus according to claim 1, wherein the optical systemcomprises at least one reflective optical element with an opening, andthe measurement beam path extends within the optical system such thatthe measurement radiation passes through the opening in the at least onereflective optical element.
 9. The apparatus according to claim 1,wherein the measurement beam path is configured to measure a position ofat least one point of the substrate surface with the measurementradiation guided by the measurement beam path.
 10. The apparatusaccording to claim 1, wherein the measurement beam path is configuredsuch that the measurement radiation is reflected on the surface of thesubstrate.
 11. The apparatus according to claim 1, wherein the surfaceof the substrate being imaged is disposed on a wafer, and themeasurement beam path is configured such that the measurement radiationis reflected on a surface of the substrate facing the optical system.12. The apparatus according to claim 1, wherein an obscuration apertureis disposed in a pupil plane of the optical system.
 13. The apparatusaccording to claim 1, wherein the measurement beam path extends at leastonce through a pupil plane of the optical system.
 14. The apparatusaccording to claim 1, wherein the measurement area is offset from theexposure area on the substrate surface in a direction parallel to thescanning direction.
 15. The apparatus according to claim 1, wherein theoptical system and the structure are configured such that themeasurement area precedes the exposure area during the exposureoperation, whereby the measurement area becomes at least one pointwithin the exposure area on the substrate.
 16. The apparatus accordingto claim 1, wherein the optical system comprises at least one reflectiveoptical element, and the measurement beam path extends within theoptical system such that the measurement radiation is reflected on theat least one reflective optical element.
 17. The apparatus according toclaim 16, wherein the measurement beam path is configured such that themeasurement radiation is reflected twice on the at least one reflectiveoptical element.
 18. A method for determining a property of anarrangement which comprises an apparatus for microlithographicprojection exposure and a substrate disposed in an exposure position ofthe apparatus, the apparatus comprising an optical system configured toimage mask structures onto a surface of the substrate by projecting themask structures with an exposure beam of imaging radiation having anextreme ultraviolet or shorter wavelength onto an exposure area of thesubstrate surface, wherein the optical system comprises at least onereflective optical element, the method comprising: performing anexposure operation with the apparatus configured as a scanner, such thatthe exposure area on the substrate surface is exposed by the exposurebeam of the imaging radiation while the substrate is moved relative tothe exposure beam in a scanning direction, thereby displacing theexposure area on the substrate surface, guiding measurement radiationwithin the optical system along a measurement beam path during theexposure operation of the apparatus, and thereby directing themeasurement radiation onto a measurement area of the substrate thatmoves on the substrate surface offset from the exposure area, anddetermining the property of the arrangement from the guided measurementradiation.
 19. The method according to claim 18, wherein the measurementradiation is guided within the optical system along the measurement beampath such that at least two optical elements of the optical system areincluded in the measurement beam path.
 20. The method according to claim18, further comprising: determining a position of at least one point ofthe substrate surface as the property during the imaging of the maskstructures onto the substrate surface.
 21. The method according to claim18, wherein at least one of the following holds true: (i) themeasurement area precedes the exposure area on the substrate; and (ii)the measurement area trails the exposure area on the substrate.
 22. Themethod according to claim 18, wherein the measurement area precedes theexposure area during the exposure operation such that a specificlocation of the measurement area at a first instant in time becomes atleast one point within the exposure area on the substrate at a secondinstant in time that follows the first instant in time.
 23. An apparatusfor microlithographic projection exposure comprising: an optical systemcomprising a plurality of optical elements and configured to image maskstructures onto a surface of a substrate by projecting the maskstructures with an exposure beam of imaging radiation having an extremeultraviolet or shorter wavelength onto an exposure area of the substratesurface, wherein the optical system is a catoptric system, and structuredefining a measurement beam path and configured to guide measurementradiation, the measurement beam path extending within the optical systemsuch that the measurement radiation impinges onto a measurement area ofthe substrate surface, wherein the apparatus is configured as a scanner,wherein during an exposure operation performed by the apparatus, theexposure area on the substrate surface is exposed by the exposure beamwhile the substrate is moved relative to the exposure beam, therebydisplacing the exposure area on the substrate surface, wherein themeasurement beam path is configured such that the measurement area isoffset from the exposure area on the substrate surface during theexposure operation, and wherein the apparatus is configured to determinea focus position for the exposure beam based on at least one point ofthe substrate surface being measured with the measurement radiationduring the exposure operation.
 24. An apparatus for microlithographicprojection exposure comprising: a catoptric optical system comprising aplurality of optical elements and configured to image mask structuresonto a surface of a substrate during an exposure operation by projectingthe mask structures with an exposure beam of imaging radiation having anextreme ultraviolet or shorter wavelength onto an exposure area of thesubstrate surface, wherein the optical system comprises at least onereflective optical element with an opening, an optical injecting elementconfigured to inject measurement radiation into the optical system, suchthat the measurement radiation passes through only a part of the opticalsystem consisting of a subset of the plurality of optical elements,during the exposure operation, and structure defining a measurement beampath and configured to guide the measurement radiation, the measurementbeam path extending within the optical system such that the measurementradiation passes through the opening in the at least one reflectiveoptical element and impinges onto a measurement area of the substratesurface, wherein the apparatus is configured as a scanner, whereinduring the exposure operation performed by the apparatus, the exposurearea on the substrate surface is exposed by the exposure beam while thesubstrate is moved relative to the exposure beam in a scanningdirection, thereby displacing the exposure area on the substratesurface, and wherein the measurement beam path is configured such thatthe measurement area moves, offset from the exposure area, on thesubstrate surface during the exposure operation.
 25. A method fordetermining a property of an arrangement which comprises an apparatusfor microlithographic projection exposure and a substrate disposed in anexposure position of the apparatus, the apparatus comprising an opticalsystem configured to image mask structures onto a surface of thesubstrate by projecting the mask structures with an exposure beam ofimaging radiation having an extreme ultraviolet or shorter wavelengthonto an exposure area of the substrate surface, wherein the opticalsystem comprises a plurality of optical elements including at least onereflective optical element with an opening, the method comprising:performing an exposure operation with the apparatus configured as ascanner, such that the exposure area on the substrate surface is exposedby the exposure beam of the imaging radiation while the substrate ismoved relative to the exposure beam in a scanning direction, therebydisplacing the exposure area on the substrate surface, guidingmeasurement radiation within the optical system along a measurement beampath during the exposure operation of the apparatus such that themeasurement radiation passes through the opening in the at least onereflective optical element and through only a part of the optical systemconsisting of a subset of the plurality of optical elements, and therebydirecting the measurement radiation onto a measurement area of thesubstrate that moves on the substrate surface offset from the exposurearea, and determining the property of the arrangement from the guidedmeasurement radiation.
 26. An apparatus for microlithographic projectionexposure comprising: a catoptric optical system comprising a pluralityof optical elements and configured to image mask structures onto asurface of a substrate during an exposure operation by projecting themask structures with an exposure beam of imaging radiation having anextreme ultraviolet or shorter wavelength onto an exposure area of thesubstrate surface, wherein the optical system comprises at least onereflective optical element with an opening, an optical injecting elementconfigured to inject measurement radiation into the optical system, suchthat the measurement radiation passes through only a part of the opticalsystem consisting of a subset of the plurality of optical elements,during the exposure operation, and structure defining a measurement beampath and configured to guide the measurement radiation, the measurementbeam path extending within the optical system such that the measurementradiation passes through the opening in the at least one reflectiveoptical element and impinges onto a measurement area of the substratesurface, wherein the apparatus is configured as a scanner, whereinduring the exposure operation performed by the apparatus, the exposurearea on the substrate surface is exposed by the exposure beam while thesubstrate is moved relative to the exposure beam, thereby displacing theexposure area on the substrate surface, wherein the measurement beampath is configured such that the measurement area is offset from theexposure area on the substrate surface during the exposure operation,and wherein the apparatus is configured to determine a focus positionfor the exposure beam based on at least one point of the substratesurface being measured with the measurement radiation during theexposure operation.